(1) Field of the Invention
This invention relates to devices such as image scanning, facsimile and etc. and particularly to the picture image signal compensation device for eliminating variations among picture elements of said devices.
(2) Description of the Prior Art
FIG. 3 is a block diagram showing a circuit construction of a conventional picture image signal compensation device.
In the drawing, (1) indicates an A/D signal converter which converts analogous picture image signals to digital picture image signals, (2) a latch which holds data temporarily, (3) a memory storage for storing said held data, and (4) a comparison calculator to compensate for picture image data by comparison of manuscript image data with the data from whiteboard stored in the memory storage 3.
Next, compensating operation of the conventional picture image signal compensating device as shown in above FIG. 3 is explained. A standard picture image signal (A') at a level of whiteboard 10 converted by the A/D converter (1) is held at the latch 2 at the time of reference at the level of the whiteboard, stored at each location of tahe memory storage 3 corresponding to each of picture elements and on completion of reference of 1 line of the white level, storing the data into the memory storage finishes also.
Next, the original manuscript image signals converted by the A/D convertor are compared proportionally with the signal data B of the picture elements at the white level stored in the memory storage 3, and picture image compensation signals C having been compensated from the original manuscript image signals A are taken out from this comparison calculator 4.
Since said conventional picture image signal compensation device is constructed as stated above, there has been a problem that the whiteboard which functions as a white level standard must be kept free from even a little dust and scratches and for this reason is necessary to be cleaned periodically.